In various electrical circuits, a protection device is incorporated into the electrical circuit in order to protect an electrical/electronic apparatus and/or an electrical/electronic part which are incorporated in the circuit or an electrical/electronic circuit when a voltage higher than the rated voltage is applied and/or a current higher than the rated current flows.
As such protection device, it has been proposed to use a bimetal switch and a PTC component which are connected in parallel to each other (see the Patent Reference below). In the circuit protection device, under a normal operating condition, i.e. under a condition in which a voltage is not more than the rated voltage and a current is not more than the rated current, substantially all current flowing through the circuit passes through contacts of the bimetal switch in their contacting states; and for example, when an excessive current flows, the bimetal part of the bimetal switch rises to a high temperature so that such contacts are separated and opened, so that the current is diverted to the PTC component. As a result, the PTC component is tripped by the excessive current to become a high-temperature and high-resistance state, and substantially interrupts the current flowing through the PTC component. At that time, the high temperature of the PTC component maintains a bimetal part at a high temperature so that the open state of the bimetal switch is maintained, that is, the latch state of the bimetal switch is maintained. In such circuit protection device, it is said that an arc does not occur at the contact of the bimetal switch since there is no need to switch the current.
Japanese Publication No. International Publication No. WO 2008/114650 is a prior patent reference.